This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This project proposes the study of transcriptional regulation in Bacillus subtilis by direct, in vivo, observation using state-of-the-art two-photon fluorescence correlation spectroscopy. The project involves the study of two transcriptional repressors from B. subtilis, CggR and CcpN. Much work has been done in vitro on CggR and CcpN (Zorrilla et al, 2007a;Zorrilla et al, 2007b;Zorrilla et al, 2008a;Zorrilla et al, 2008b) since their discovery in the sequencing of the B. subtilis genome(Kunst et al, 1997). Both transcriptional repressors control opposite directions in the carbon metabolic cycle in gram positive bacteria through the production of metabolic enzymes. We propose to directly observe transcriptional regulation in vivo at the single molecule level. Using genetically engineered strains of B. subtilis, containing fluorescent protein fusions with CggR, CcpN and related factors under native promoters, we will apply the techniques of point and scanning two photon fluorescence correlation spectroscopy (FCS and sFCS), Number and Brightness (N&B) and raster image correlation spectroscopy (RICS). We will elucidate mechanisms of transcriptional regulation that cannot be observed by in vitro investigation.